Boolean modifier difference not engraving correctly
You have some problems because you need to clean up a bit your meshes:


Select your symbol object, go in Edit mode, select all and W > Remove Doubles.
Also press X > Limited Dissolve.
Select your cylinder, go in Edit mode, select all and W > Remove Doubles.
Give your cylinder a Boolean modifier, choose Operation > Difference, and select your symbol as Object.
It works (well, it will need a bit of topology work)